N.P.
My nearly four year old has been this way her whole life. When she first learned how to walk and we would go outside for little outings, a car parked in the driveway next to us and she bolted over there. The man got out of the car and she held her arms up to him to be picked up and this perfect stranger, as I was running up to her, just scooped her up and walked the rest of the way to me to pass her over. His parting words were, "It's dangerous to let your daughter go to just anyone!"
Well, duh.
She has no concept of stranger danger or personal space. Every day we talk about what makes someone a stranger to us and how we behave when we meet strangers. She used to ask to pet people. She had a thing for hair and would love to pet peoples heads. She'd ask everyone if she could pet their hair. At the playground she'd just pet kids and giggle.
And oh lord the hugging. HUGGING everyone. Other kids are running behind their mother's legs and hiding from her and she's still trying to give them hugs.
For a while I just stopped going out to public places with lots of people because I was sick of trying to make her understand that not everyone she meets is family, because she treated EVERYONE like they were family. Snuggled with them, kissed and hugged them. Petted their heads and said, "Aww good girl! It tickles!"
She's finally starting to understand at nearly four, about boundaries. When she was at baby birthday parties and started to become overly affectionate with kids she didn't know well or adults we didn't know I would be on hand to divert her attention to a toy or something else. It was the only way to keep her from annoying the spit out of people who didn't appreciate the attention.
Being hyper vigilant to divert her or just staying home and away from others until she grows up a bit more were my only options. It's a joy and a pleasure to have such a sweet and loving kid but it's also socially awkward (and terrifying in some situations).